Abstract :
[en] Many micropollutant products are introduced into the environment by domestic, industrial or hospital waste waters. It has been observed that many of them are not well removed by traditional biological waste water treatment plants (WWTP). In this project, a physico-chemical process is elaborated and placed at the end of existing WWTP. Such processes already exist and are based on an ozone and UV radiation combination to oxidize organic compounds. Our study shows that higher degradations could be reached using heterogeneous photocatalysis in addition to ozone and UV radiation.
At the laboratory scale, problematic micropollutants of the European Water Framework Directive have been chosen to model waste water (10 μg/L): pharmaceuticals (diclofenac, carbamazepin, sulfamethoxazol), PFOS, anti-corrosive (1H-Benzotriazol), phthalate (DEHP), alkylphenol (bisphenol A), pesticide (diuron, atrazine), flame retardant (PBDE). Their degradations were evaluated by LC-MS/MS and GC-MS/MS.
Different photocatalysts have been synthesized by organic and aqueous sol-gel methods and deposited as thin films by dip-coating on glass substrate: pure titanium dioxide (TiO2) and doped titanium dioxide (with Ag, Pt, Commercial Evonik P25, MnO2 - nanoparticles, and with Zn2+ ions). Characterizations were made by profilometry for films thickness and roughness, by GIRXD for photoactive crystalline phase presence, by UV-Vis transmission for band-gap, by ICP-AES/MS for dopants percentages in films and in water (leaching concentration through delamination). The photoactivity of all these catalysts were determined from the degradation on 10 micropollutants (10 µg/L) under UV-C for 1 h.
The best photocatalyst found was silver doped titanium dioxide. A film was then deposited inside a one-meter long alkaline-free tube for pilot trials. Experiments were carried out with 150 L of our model water (10 micropollutants with 10 µg/L) and with 150 L of waste water at the exit of a WWTP. Both experiments have confirmed laboratory results for efficient degradation of pharmaceutical products in water.